This invention relates to a toning unit and separator method and apparatus especially for use with ion deposition printers utilizing a single component magnetic toner.
Although not so limited, this invention has been developed for use with an ion deposition printer using a print engine produced by Delphax Systems of Mississauga, Canada. In ion deposition printing, a digitally controlled input-output module places a charge pattern corresponding to the desired image onto the dielectric surface of a rotating, cylindrical image drum by use of an ion projection or print cartridge. Characters and other images are formed when the charged ions are arranged in a latent electrostatic dot matrix pattern on the surface of the drum. U.S. Pat. No. 4,619,515, granted to Maczuszenko et al. on Oct. 28, 1986, shows a representative ion deposition printer of the type with which this invention may advantageously be used.
Adjacent the rotating image drum there is a toning unit assembly that constitutes a source of single component toner which is attracted to the ion-charged areas of the drum. The toning unit assembly includes a housing including a toner hopper having an inlet opening to enable the toner to be poured into the hopper, an outlet opening at its lower end, a screen partly closing the outlet opening, and means for conveying toner from the hopper to the image drum including an agitator member in the bottom of the hopper that both agitates the toner in the hopper and forces toner downwardly through the screen in the outlet opening, and a rotatably-driven magnetic toner roller (for convenience termed a "toner feed roller" herein) positioned below the outlet opening to receive toner passing through the screen. A rotatably-driven second magnetic toner roller (termed a "toner applicator roller" herein) may be mounted between the toner feed roller and the image drum. The toner applicator roller receives toner from the feed roller and positions the toner for transfer to ion-charged areas of the image drum. One or more additional toner applicator rollers could also be used.
After developing the image on the drum as described above, a process called transfixing is used to transfer the toner from the drum to the paper on which the ultimate image is to be formed. In transfixing the toner and the paper are pressed together between the image drum and a pressure roller, at which time essentially all of the toner adheres to the paper.
Traces of toner remaining on the drum after transfixing are cleaned away by use of a scraper blade that scrapes any toner particles and paper dust clinging to the drum and collects them in a catch tray beneath the scraper blade. An electrostatic erase rod erases or neutralizes any charge remaining on the drum.
A preferred toner for use in ion deposition printing comprises particles of magnetic iron oxide coated with carbon black and a lubricant comprising zinc stearate. Pigmentatious material other than carbon black may be used but are not, as yet, in common use. The zinc stearate is a non-magnetic lubricant that enhances the flow characteristics of the toner and minimizes the formation of large clumps or agglomerates of toner.
Although ion deposition printers are commercially successful, and offer substantial advantages for many printing applications, experience with such printers indicates that the costs of replacement of consumable parts adds significantly to the cost of operating them. Parts that may be classed as consumables since they require frequent replacement or repair include the erase rod, the print cartridge, the image drum, and the scraper blade.
A further problem with existing ion deposition printers resides in the frequency with which the toning unit assemblies must be cleaned. When running high volumes of printing, the toning unit assemblies may have to be cleaned as often as two or three times during each eight hour shift.
Accordingly, there is a need to improve ion deposition printers to lower the cost of operation thereof by reducing the frequency with which the above noted consumables need repair or replacement, and it is an object of this invention to provide such an improved printer.
A further object of this invention is to reduce the frequency with which parts of the toning unit assembly require cleaning.
In accordance with this invention, the above objects are obtained by use of an improved method of toner delivery that includes the separation of substantial amounts of the non-magnetic (zinc stearate) particles, and perhaps magnetic particles that are so poorly attracted by magnets of the feed roller that they are effectively non-magnetic, from the toner before the toner is transferred to the image drum, and by removing the separated non-magnetic and poorly magnetic particles (jointly termed "unwanted particles" herein) from the toning unit assembly. Such separation is accomplished by providing a partly closed unwanted particle chamber extending substantially along the entire width of the hopper adjacent and below the feed roller and generally below the hopper outlet. A source of negative air flow is established across substantially the entire width of the hopper, and correspondingly across the entire length of the unwanted particle chamber, to draw the unwanted particles from the unwanted particle chamber to the source of the negative air flow. An air flow is thus created around the toner feed and applicator rollers to assist gravity in pulling the unwanted particles downwardly to the bottom of the toning unit housing and is effective to draw away a substantial portion of the unwanted particles from the toner.
By the simple expedient of separating and removing the unwanted particles from the toner in this fashion, a substantial improvement in the operation of an ion deposition printer may be obtained. In particular, the frequency with which the aforementioned consumables need replacement is dramatically reduced. Tests have indicated that the consumables lives are conservatively doubled and in some cases quintupled or more. Of course, it is to be expected that the improved characteristics will depend on the nature of the printing being done and the care taken by the operator to provide regular maintenance, such as simple cleaning operations.
A further object of this invention is to provide a toning unit assembly with an air manifold assembly including a plenum chamber opening adjacent the feed roller to the unwanted particle chamber, and to provide for the connection of a source of negative air pressure to the plenum chamber for separating the unwanted particles from the feed roller and from the unwanted particle chamber below the toner hopper outlet. The air manifold may be permanently installed on the toning unit housing but is preferably readily removably mounted on the rear of the toning unit housing so that convenient access may be had to the air manifold assembly and other parts of the toning unit assembly.
A more specific object is to provide such an air manifold assembly that does not substantially increase the dimensions of the toning unit assembly and that is lightweight. The size of the air manifold assembly is usually an important consideration because of the restrictions on available space among other parts of the printer, especially the paper feeding mechanism. A light weight air manifold is desirable so that the mounting of the toning unit assembly, which mounting is usually adjustable, will not be disturbed because of the added weight of the air manifold assembly.
Another object of this invention is to partly close the unwanted particle chamber by the rear wall of the air manifold assembly and by a collector plate provided on the bottom of the feed assembly so that particles from the toner are prevented from falling downwardly out of the feed assembly and to increase the efficiency with which the unwanted toner particles are removed from the collection chamber.
The air manifold assembly of this invention comprises a thin housing defining a plenum chamber open to a front wall backing up and substantially parallel to the rear wall of the toning unit housing. The manifold housing further includes a rear wall having a exhaust port at its upper end. The lower ends of the manifold housing front and rear walls are spaced apart to provide an inlet opening to the collection chamber. The exhaust port is preferably connected by hose to a blower located remotely from the toning unit assembly. To prevent the toner particles from fouling the atmosphere, the blower is preferably mounted in a housing having filters for cleaning the unwanted toner particles from the air drawn from the feed assembly.
The practice of this invention results in a cleaner atmosphere in and around the printer which may avoid the need to replace electronic components which otherwise may become coated and then damaged due to overheating. Use of the invention also minimizes freckling encountered in printing large dark areas. It has also been found to avoid the formation of gray areas or lines on the back of the printed paper, believed to be caused by toner transfering from the print drum to the pressure roller and then from the pressure roller to the back sides of the paper that is subsequently printed. Apparently for the same reason, acceptable quality duplex printing has not been feasible with the known ion deposition printers, but good quality duplex printing may be obtained with printers equipped with a toning unit assembly in accordance with this invention.
Use of this invention also results in the improvement of the quality of the printing obtained by ion deposition printers, particularly with regard to improvements in the sharpness of the definition and contrast obtainable.
Other objects and advantages of this invention will become apparent from the following description and the drawings.